Wheel mount assemblies in general are well known in the art for use with many different types of wheeled devices. Such wheel mount assemblies are commonly employed for mounting the rear wheels on a typical wheelchair. Each wheel mount assembly typically incorporates a number of adjustments that allow the wheelchair occupant to customize the wheelchair to his or her body proportions, body mechanics, and driving conditions. Frequently, the rear wheels of the wheelchair are cambered, or angled with respect to a vertical plane. A wheelchair with a large camber angle has more responsive turning, which is typically beneficial in sports applications. A wheelchair with a little to no camber angle has a smaller overall width and thus greater manoeuvrability in tight confines. Often the wheels can be adjusted so that their camber angle can be changed from 0 degrees to 12 degrees, or sometimes substantially more, where the top of the wheel is closer to the chair than the bottom of the wheel.
Some wheelchairs provide the ability to adjust the fore/aft position of the rear wheel with respect to the wheelchair frame. Such adjustment is known as a “center-of-gravity” adjustment. Shifting the rear wheels rearward produces a more stable wheelchair that is less likely to tip backwards. Shifting the rear wheels forward makes the wheelchair easier to balance on the rear wheels. This helps with manoeuvrability over obstacles, such as curbs, where the wheelchair occupant must lift the front casters off the ground in order to traverse the obstacles.
When an adjustment is made to the rear wheel camber angle the rear height of the wheelchair may also change, which may in turn cause the rear wheels to toe-in or toe-out. That is to say, the rear wheels become misaligned with respect to the frame. This misalignment is undesirable because it increases rolling friction. If the act of decreasing the camber angle raises the rear wheel height, the rear wheels may toe-in. Conversely, increasing the rear wheel camber angle typically lowers the rear wheel height, which may cause the rear wheels to toe-out. To correct toe-in or toe-out, the mounting hardware that attaches the rear wheels to the wheelchair frame must allow the axles of the rear wheel to rotate in order to re-align the camber angle with respect to a vertical sagittal plane. Alternatively, the height of either the rear wheels or the front caster wheels may be changed to adjust the toe-in or toe-out of the drive wheels as well as to keep the main pivot axis of each of the caster wheels vertical.
With some conventional wheelchairs that offer adjustable camber (although note that in many wheelchairs the camber angle is fixed), the camber adjustment takes the user a significant amount of time. Adjusting the camber often requires removing quite a number of parts and adding or subtracting washers or other spacers to achieve the proper angle. Alternatively adjusting the camber may entail needing different camber inserts each with fixed angles. Even when done by a trained technician, the process may still take considerable time.
In some wheelchairs that provide easier means of changing camber angle and center gravity adjustment, often the result is an overly flexible wheelchair frame. A wheelchair that lacks rigidity or is overly flexible typically has reduced performance, may feel cumbersome or un-safe, and may be more prone to breakage.
While many wheelchairs provide wheel camber angle, toe-in, toe-out, and center of gravity adjustability, there is a need for a lightweight, user-friendly adjustment design that minimizes parts, complexity, and adjustment difficulty while at the same time providing adequate rigidity and performance.